1. Field of the Invention
The present invention relates to a spindle head unit incorporating a spindle drive motor that has a rotor assembly rotably mounted on a spindle and a stator assembly fixedly arranged outside the rotor assembly. More particularly, the present invention relates to a spindle head unit having an improved structure enabling avoidance of thermal deformation of the spindle head unit due to heat from the spindle drive motor, when the spindle head unit is accommodated in diverse kinds of machine tools and operated for long periods of time.
2. Description of the Prior Art
Spindle head units incorporating drive motors, particularly, AC motors, for driving the spindles have come into wide use since they do not require rotation transmitting mechanisms and other auxiliary mechanisms between the spindles of the machine tools and the drive motors. Such motor-incorporated spindle head units, however, suffer from thermal deformation to their spindles, bearing boxes, outer casings, and other mechanical elements due to heat generated from their drive motors. As a result, use of such spindle head units for machining with cutting tools or workpiece holders attached thereto inevitably results in low machining accuracy.
It has been understood that to prevent thermal deformation of mechanical element of motor-incorporated spindle head unit, some appropriate cooling system has to be provided therein to remove the heat from the drive motor, especially, the stator assembly of the AC drive motor. Up until now, however, no concrete designs have been proposed for motor-incorporated spindle head units having built-in compact cooling systems.
Here, it should be understood that a cooling system assembled in a motor-incorporated spindle head unit has to also effectively prevent direct transmission of large amounts of heat generated from the excitation windings of the stator assembly of the drive motor to the mechanical elements, especially the front part of the spindle. This is because if such heat is directly transmitted to the front part of the spindle, not only the spindle itself but also the cutting tools or the workpiece holders will be subjected to thermal deformation, resulting in low machining accuracy.